Review

class IndexReader {
  /** Expert: returns an IndexReader reading the index in
   *  the given Directory, with a custom {@link
   *  IndexDeletionPolicy}.  You should pass readOnly=true,
   *  since it gives much better concurrent performance,
   *  unless you intend to do write operations (delete
   *  documents or change norms) with the reader.
   * @param directory the index directory
   * @param deletionPolicy a custom deletion policy (only used
   *  if you use this reader to perform deletes or to set
   *  norms); see {@link IndexWriter} for details.
   * @param readOnly true if no changes (deletions, norms) will be made with this IndexReader
   * @param termInfosIndexDivisor Subsamples which indexed
   *  terms are loaded into RAM. This has the same effect as {@link
   *  IndexWriter#setTermIndexInterval} except that setting
   *  must be done at indexing time while this setting can be
   *  set per reader.  When set to N, then one in every
   *  N*termIndexInterval terms in the index is loaded into
   *  memory.  By setting this to a value > 1 you can reduce
   *  memory usage, at the expense of higher latency when
   *  loading a TermInfo.  The default value is 1.  Set this
   *  to -1 to skip loading the terms index entirely.
   * @throws CorruptIndexException if the index is corrupt
   * @throws IOException if there is a low-level IO error
   */
  public static IndexReader open(final Directory directory, IndexDeletionPolicy deletionPolicy, boolean readOnly, int termInfosIndexDivisor) throws CorruptIndexException, IOException {
    return open(directory, deletionPolicy, null, readOnly, termInfosIndexDivisor);
  }

}